2017_Bacteria-Viruses_STQ_MS

2017 Bacteria and Viruses STQ MS 2017 / H2 / ACJC PRELIM / P2 Q8 (BE)1Speciation events have been observed to occur very frequently in bacteria. It was suggested that the high rate of speciation is due to the high level of variation in bacteria.(a)Transformation and conjugation are two processes which increase the level of variation in bacteria. Distinguish these two processes. ConjugationTransformationGenetic material being transferred1.Transfers the F plasmid or R plasmid1.Transfers fragments of the bacterial chromosome;Donor cell2.Donor cells are F+ cells / carries the F plasmid or R plasmid;2.Donor cells may be lysed cells that releases its DNA;Recipient cell3.Recipient cells are F- cells / do not carry the F plasmid or R plasmid;3.Recipient cells must be competent / secrete the competence factor;Physical contact4.Direct physical contact required between two cells through sex pilus;4.No physical contact required between cells / exogenous DNA taken up directly by recipient cell; [3]Bacterial evolution is one of the most dynamic and exciting areas in current biological research. Over the years, a barrier in this field of research is the difficulty in classifying bacterial species. However, in recent times, new analytical tools in molecular biology have offered new insights into the classification of bacterial species.(b) (i) Suggest why scientists had difficulties in the classification of bacterial species. 1.Bacteria reproduce asexually / by binary fission;2.Unable to determine between species according to biological species concept / bacteria are unable to interbreed to produce fertile viable offspring;3.Horizontal gene transfer/transformation/conjugation between relatively distantly related bacteria / different bacterial species (OWTTE);4.Results in high rates of recombination, making it difficult to determine a single species;5.Different species may be morphologically similar;[2](ii)Explain how analytical molecular tools have helped overcome this barrier in research.1. Molecular tools have helped determine genetic sequences of bacteria / compare genetic sequences of bacteria;2. Allowing scientists to classify bacteria according to genetic distance / phylogenetic distance;3.Provides an objective method (to determine genetic distance);4.Data obtained is quantitative;5.Hence more sensitive to differences between species / data could be used for statistical analyses;[2]

(c)The outer layers of the two types of bacteria with peptidoglycan cell walls known as Gram-positive and Gram-negative bacteria are shown in Fig. 8.1 below. Penicillin is an antibiotic that is known to be effective against only one of the two types of bacteria above.With reference to the information given and your own knowledge, deduce which type of bacteria is susceptible to the action of penicillin and explain why.1. Penicillin is effective only against gram-positive bacteria;2. Gram-negative bacteria have an outer membrane (and lipoproteins) (that surrounds the peptido